Apparatuses including electrodes having a conductive barrier material and methods of forming same

ABSTRACT

Apparatuses and methods of manufacture are disclosed for phase change memory cell electrodes having a conductive barrier material. In one example, an apparatus includes a first chalcogenide structure and a second chalcogenide structure stacked together with the first chalcogenide structure. A first electrode portion is coupled to the first chalcogenide structure, and a second electrode portion is coupled to the second chalcogenide structure. An electrically conductive barrier material is disposed between the first and second electrode portions.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.13/776,485 filed Feb. 25, 2013 and issued as U.S. Pat. No. 9,166,158 onOct. 20, 2015. The aforementioned application, and issued patent, isincorporated herein by reference, in its entirety, for any purpose.

TECHNICAL FIELD

Embodiments of the invention relate generally to integrated circuits,and more particularly, in one or more of the illustrated embodiments, toelectrode structures for phase change memory cells that include aconductive barrier material for phase change memory cells, for example.

BACKGROUND OF THE INVENTION

Many advancements have contributed to a recent surge in phase changememory development. With reference to FIG. 1, one recent improvementthat has resulted in a simplified and lower cost method of manufacturingphase change memory cells is the inclusion of a switch 124, such as aselectable diode or an ovonic threshold switch, together with a phasechange memory storage element 122 in a stacked memory cell 120 of anapparatus 100. Adding the switch 124 within each stacked memory cell 120eliminates the need to form a transistor switch in the semiconductorsubstrate below or above each respective memory cell 120.

In order to prevent heat transfer between the phase change memorystorage element 122 and the switch 124, however, a thermally insulativeelectrode 130 such as carbon is typically positioned between the phasechange memory storage element 122 and the switch 124. The carbonelectrode 130 provides good electrical conductivity (for voltages andcurrents to pass through), but inhibits the transfer of thermal energybetween the phase change memory storage element 122 and the switch 124.The carbon electrode 130 may also serve as a diffusion barrier toprevent diffusion of materials between the phase change memory storageelement 122 and the switch 124 during manufacture and operation of thememory cell 120.

Some manufacturing processes of depositing the carbon 130 (or othermaterial), such as physical vapor deposition (PVD), may cause the carbon130 to form in a columnar manner. Such a columnar carbon electrode 130,however, provides a poor diffusion barrier because the columnarityallows various materials to diffuse across the electrode 130. Forexample, oxygen, indium, selenium, and so forth may diffuse from thephase change memory storage element 122 to the switch 124, or viceversa, during manufacturing—for example during deposition, etching,thermal cycling and annealing, and/or electrical cycling—or duringoperation of a finished and packaged memory device. This diffusion ofvarious materials across the electrode 130 may lead to degradation and,eventually, to premature failure of a memory device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plurality of phase change memory cellsaccording to the prior art.

FIG. 2 is a perspective view of a plurality of phase change memory cellsaccording to an embodiment of the present invention.

FIG. 3 is a perspective view of a plurality of phase change memory cellsaccording to an embodiment of the present invention.

FIG. 4 is a perspective view of a plurality of phase change memory cellsaccording to an embodiment of the present invention.

FIG. 5 is a perspective view of a plurality of phase change memory cellsaccording to an embodiment of the present invention.

FIG. 6 is flow diagram of a method of manufacturing a phase changememory cell according to an embodiment of the present invention.

FIG. 7 is a block diagram of a memory according to an embodiment of theinvention.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the invention. However, it will be clearto one skilled in the art that embodiments of the invention may bepracticed without these particular details. Moreover, the particularembodiments of the present invention described herein are provided byway of example and should not be used to limit the scope of theinvention to these particular embodiments. Furthermore, the drawingsprovided herein are not necessarily drawn to scale, including thethicknesses of the various layers relative to one another. Also,relative and directional references (e.g., above, below, etc.) are givenby way of example to aid the reader's understanding of the particularembodiments described herein, and should not be read as requirements orlimitations unless specifically set forth in the claims.

FIG. 2 illustrates an apparatus 200 including an array 202 of phasechange memory cells 220 according to an embodiment of the invention. Asused herein, apparatus may refer to, for example, an integrated circuit,a memory device, a memory system, an electronic device or system, asmart phone, a tablet, a computer, a server, etc. Each of the memorycells 220 in the apparatus 200 includes a phase change device 222 and aswitch 224, both of which may be chalcogenide structures. For example,in one embodiment, the phase change device 222 may be a phase changestorage element that is configured to store one or more bits of databased on the phase (e.g., amorphous, partially crystalline, crystalline,etc.) and thus the electrical resistance of a chalcogenide material. Theswitch 224 may be a selectable diode or ovonic threshold switch, and maybe configured to allow read and/or program access to the phase changedevice 222. In another embodiment, additional phase change devices (notillustrated in FIG. 2) or chalcogenide structures may be included withineach stacked memory cell 220. Also, although the phase change device 222is illustrated as being above the switch 224 in FIG. 2, in otherembodiments, the phase change device 22 may be positioned below theswitch 224.

Both of the phase change device 222 and the switch 224 may include aportion of chalcogenide glass, such as GeSbTe, which may be changedbetween any number of amorphous, partially crystalline, and/orcrystalline states depending on voltages and/or currents provided to thephase change device 222 and the switch 224. Also, both of the phasechange device 222 and the switch 224 are integrally formed within eachmemory cell 220, or in other words, both of the phase change device 222and the switch 224 are stacked together in each memory cell 220, asopposed to having a switch formed underneath or above the memory cell220 for example.

The memory array 202 includes a plurality of access lines 250, 270, andeach memory cell 220 includes a plurality of access line electrodes 223,225 configured to couple the memory cells 220 to the plurality of accesslines 250, 270. A first set of access lines 250 may be bitlines operableto select individual bits within words of the array 202. Each memorycell 220 may include a first access line electrode 223 between the phasechange device 222 and a respective one of the first set of access lines250. A second set of access lines 270 may be wordlines operable toselect one or more bits within individual words of the array 202. Eachmemory cell 220 may include a second access line electrode 225 betweenthe switch 224 and a respective one of the second set of access lines270. Together, the two sets of access lines 250, 270, and the respectiveelectrodes 223, 225 on each of the memory cells 220 provide theelectrical coupling for access control circuitry (not illustrated inFIG. 2) to read and program the memory cells 220.

Each of the access lines 250, 270 may be formed of an electricallyconductive material, such as copper, aluminum, polysilicon, and soforth. The access lines 250, 270 may also be comprised of titanium,tungsten, a nitride of titanium or tungsten, or some combination ofthese. Each of the electrodes 223, 225 may be formed of an electricallyconductive material and/or a thermally insulative material. In someexamples, the electrodes 223, 225 may be formed from carbon and maycouple the memory cells to the respective access lines 250, 270.

Each memory cell also includes one or more electrode portions 230 a, 230b positioned between the phase change device 222 and the switch 224.Each electrode portion 230 a, 230 b may be between approximately 5-150angstroms (Å) thick in some embodiments.

With reference to FIG. 2, a first electrode portion 230 a may bedisposed between the phase change device 222 and the switch 224proximate the phase change device 222, and a second electrode 230 b maybe disposed between the switch 224 and the phase change device 222proximate the switch 224. The first and second electrode portions 230 a,230 b may in some instances be referred to as first and secondelectrodes 230 a, 230 b, or as first and second electrode portions 230a, 230 b of the same electrode which are separated by an intermediarybarrier material 240 as explained in more detail below. That is, anelectrode may include the first and second electrode portions 230 a, 230b and the intermediary barrier material 240.

The first and second electrode portions 230 a, 230 b (or the first andsecond electrodes 230 a, 230 b) disposed between the phase change device222 and the switch 224 may provide electrical conductivity and thermalinsulation between the phase change device 222 and the switch 224. Forexample, the first and second electrode portions 230 a, 230 b may insome embodiments have a thermal conductivity between approximately0.5-10 Wm⁻¹K⁻¹ in some examples, and may have an electrical resistivityof between 1-100 Ohm-cm as deposited (and 5-50 milliOhm-cm after a hightemperature anneal) in some examples. The electrical conductivityprovided by the first and second electrode portions 230 a, 230 b mayallow electrical voltages and currents to pass between the phase changedevice 222 and the switch 224 in order to, for example, read and/orprogram one or both of the phase change device 222 and/or the switch224. The thermal insulation provided by the first and second electrodeportions 230 a, 230 b may help prevent heat from passing through theelectrode portions 230 a, 230 b, in order to inhibit heat used inreading and/or programming one of the phase change device 222 and/or theswitch 224 from being transferred to the other of the phase changedevice 222 and/or the switch 224.

The electrode portions 230 a, 230 b may further provide a diffusionbarrier between the phase change device 222 and the switch 224, asdescribed above. However, in some cases, one or more of the electrodeportions 230 a, 230 b may have a columnar structure that reduces theeffectiveness of the electrode portions 230 a, 230 b as a diffusionbarrier. Thus, with reference to FIG. 2, a barrier material 240 that iselectrically conductive may be disposed between the first and secondelectrode portions 230 a, 230 b in some examples to help strengthen thediffusion barrier.

The electrically conductive barrier material 240 may provide electricalconductivity between the first and second electrode portions 230 a, 230b, and therefore also between the phase change device 222 and the switch224. The electrically conductive material 240 may or may not bethermally insulative. The electrically conductive material 240 may notchange the thermally insulative properties and behavior of the first andsecond electrode portions 230 a, 230 b—in other words, the electricallyconductive barrier material 240 may not alter the thermal insulationprovided by the first and second electrode portions 230 a, 230 b betweenthe phase change device 222 and the switch in some embodiments.

The electrically conductive barrier material 240 may not be reactive tothe electrode portions 230 a, 230 b (which may be formed of carbon) insome examples. For example, titanium nitride (TiN), Tungsten silicide(WSi_(x)), silicon (Si), or combinations thereof may be used in theelectrically conductive barrier material 240 in some embodiments. TiN,if used, may have a resistivity of approximately 75-300 μOhm-cm and mayhave a thermal conductivity of approximately 30 Wm⁻¹K⁻¹. WSi_(x), ifused, may have a resistivity of approximately 400-1000 μOhm-cm and mayhave a thermal conductivity of approximately 15 Wm⁻¹K⁻¹. Si, if used,may have a resistivity of approximately 50-100 Ohm-cm (when undoped) andmay have a thermal conductivity of approximately 149 Wm⁻¹K⁻¹. When Si isused in the electrically conductive barrier material 240, it may bedoped Si (e.g., it may be doped with boron, which may not be activated).While Si does provide for electrical conductivity, it may only besemiconductive in some examples, depending on the dopant and dopingconcentration. In some embodiments, the electrically conductive barriermaterial 240 may not include any type of dielectric material (e.g.,oxide). In other examples, however, the electrically conductive barriermaterial 240 may react to one or more electrode portions 230 a, 230 b.

The electrically conductive barrier material 240 may be relativelythin—it may be, for example, between 5 and 50 angstroms (Å) thick. Insome embodiments, the thickness of the electrically conductive barriermaterial 240 may be 5 Å, 10 Å, 30 Å, 45 Å, 50 Å, and so forth.

The electrically conductive barrier material 240 may be depositedamorphously in some embodiments, and/or may be amorphous duringoperation of the apparatus 200. The amorphous nature of the electricallyconductive barrier material 240 may help strengthen the diffusionbarrier between the phase change device 222 and the switch 224 becauseit mitigates the columnar structure of the electrode portions 230 a, 230b. In other words, the electrically conductive barrier material 240helps prevent diffusion between the phase change device 222 and theswitch 224 because it “breaks” any columnarity or columnar growth of thefirst and/or second electrode portions 230 a, 230 b (e.g., by causingthe columns to not be aligned), thereby reducing the diffusion pathwaysthrough the first and/or second electrode portions 230 a, 230 b. In thismanner, even if an element such as indium diffuses from one of the phasechange device 222 or the switch 224 into the columns of one of theelectrode portions 230 a, 230 b, the diffusing material will be stoppedor at least significantly hindered from passing all the way through tothe other of the phase change device 222 or the switch 224 because ofthe barrier provided by the electrically conductive barrier material240. As a result, fewer materials may diffuse between the phase changedevice 222 and the switch 224, which may lead to increased reliabilityand increased lifespan of the apparatus 200 in some examples.

In other embodiments, however, the electrically conductive barriermaterial 240 may be at least partially crystalline (e.g., TiN may be atleast partially crystalline). In these embodiments, the grain boundariesof the electrically conductive barrier material 240 may not line up withthe grain boundaries of the first and second electrode portions 230 a,230 b, in order to help prevent diffusion between the phase changedevice 222 and the switch 224. In these embodiments where theelectrically conductive barrier material 240 is at least partiallycrystalline, the electrically conductive barrier material 240 may have asubstantially different crystalline structure than the first and secondelectrode portions 230 a, 230 b.

Still referring to FIG. 2, in some embodiments, the phase change device222 and the switch 224, together with the first and second electrodeportions 230 a, 230 b, and the electrically conductive barrier material240 may define a stacked memory cell 220, which may have a substantiallyuniform cross section (e.g., within the stacked memory cell 220, no oneportion ‘sticks out’ from the stack anymore than any of the otherportions). In other examples, however, one or more of the phase changedevice 222, the switch 224, the first and second electrode portions 230a, 230 b, and the electrically conductive barrier material 240 may havedifferent cross sectional shapes and/or areas. For example, theelectrically conductive barrier material 240 may have a larger crosssection than the first and/or second electrode portions 230 a, 230 b andmay thus ensure complete partitioning of the first and second electrodeportions 230 a, 230 b from each other in order to provide a strongdiffusion barrier.

Comparing now FIG. 2 with FIG. 1, the combined thickness of the firstand second electrode portions 230 a, 230 b together with theelectrically conductive barrier material 240 in FIG. 2 may beapproximately the same as the thickness of the electrode 130 in FIG. 1in some examples. Also the combined resistance of the first and secondelectrode portions 230 a, 230 b together the electrically conductivebarrier material 240 in FIG. 2 may be approximately the same as theresistance of the electrode 130 in FIG. 1 in some examples. In otherexamples, and as explained in more detail below, the overall thicknessand/or the resistance of the first and second electrode portions 230 a,230 b and the electrically conductive barrier material 240 in FIG. 2 maybe different than the thickness and/or resistances of the electrode 130in FIG. 1.

In operation, the apparatus 200 selectively provides control signals tothe two sets of access lines 250, 270 in order to read and/or programone or both of the phase change device 222 and/or the switch 224 of thememory cells, similar to the operation of the apparatus 100 illustratedin FIG. 1. However, because the diffusion barrier between the phasechange device 222 and the switch 224 of some or all of the memory cells220 has been strengthened by the electrically conductive barriermaterial 240, fewer or no materials may diffuse across the phase changedevice 222 and the switch 224 during manufacturing—for example duringdeposition, etching, thermal cycling and annealing, and/or electricalcycling—or during operation of a finished and packaged memory device,thereby improving the reliability and usable life of the apparatus 200.

FIG. 3 illustrates an apparatus 300 including an array 302 of phasechange memory cells 320 according to an embodiment of the invention. Theapparatus 300 illustrated in FIG. 3 may generally be similar to theapparatus 200 illustrated in FIG. 2 (and like reference numerals mayrefer to similar elements), but the electrically conductive barriermaterial 340 in FIG. 3 is thicker than the electrically conductivebarrier material 240 illustrated in FIG. 2. Providing a thickerelectrically conductive barrier material 340 as illustrated in FIG. 3may provide an even stronger diffusion barrier because if, for example,the electrically conductive material 340 is amorphous, the thickerbarrier material 340 provides an even thicker structure through whichdiffusing materials would have to pass through in order to successfullydiffuse from one of the phase change device 322 and the switch 324 tothe other. Depending on the material or materials used for theelectrically conductive barrier material 340, the thicker barriermaterial 340 may also provide for different resistivities of thematerial 340. In some embodiments, and as illustrated in FIG. 3, thefirst and second electrode portions 330 a, 330 b may be thinner in orderto maintain the same overall thickness of the two electrode portions 330a, 330 b together with the electrically conductive material 340 ascompared with FIG. 2, whereas in other embodiments, the electrodeportions 330 a, 330 b may not be thinner and the overall thickness ofthe two electrode portions 330 a, 330 b together with the electricallyconductive material 340 may be greater than in FIG. 2. In general, thethicknesses of the first and second electrode portions 330 a, 330 b andthe thickness of the electrically conductive barrier material 340 mayvary from one embodiment to another, and need not necessarily be thesame and the overall thickness of the two electrode portions 330 a, 330b together with the electrically conductive material 340 need not be thesame amongst different embodiments either.

FIGS. 4 and 5 illustrate apparatuses 400, 500 including an array 402,502 of phase change memory cells 420, 520 according to embodiments ofthe invention. The apparatus 400 illustrated in FIG. 4 may generally besimilar to the apparatus 200 illustrated in FIG. 2 (and like referencenumerals may refer to similar elements), but whereas a single continuousportion of electrically conductive barrier material 240 is disposedbetween the first and second electrode portions 230 a, 230 b in FIG. 2,two, discontinuous portions 440 a, 440 b of electrically conductivebarrier material may be disposed between the first and second electrodeportions 430 a, 430 b in some embodiments as illustrated in FIG. 4. Inother words, the single portion of electrically conductive barriermaterial 240 in FIG. 2 may be partitioned into a plurality of portionsto form the barrier material portions 440 a, 440 b in FIG. 4. Ingeneral, any number of portions (e.g., 440 a, 440 b) of electricallyconductive material may be used, such as 2, 3, 4, 5 or more. Theportions 440 a, 440 b may be formed from similar or different materials.For example, both portions 440 a, 440 b may include TiN, or the firstportion 440 a may include TiN while the second portion 440 b may includeSi. The two portions 440 a, 440 b may be formed together in situ, oneafter the other (e.g., deposited without an air break), or one of theportions 440 a may be formed after some sort of break duringmanufacturing.

In some examples, the two discontinuous portions of electricallyconductive barrier material 440 a, 440 b may be contiguous to oneanother (e.g., separate, but touching), whereas in other embodiments,and with reference to FIG. 5, the first and second portions ofelectrically conductive barrier material 540 a, 540 b may be separatedby a third electrode 530 c. In other words, a third electrode 530 c maybe disposed between the first and second electrode portions 530 a, 530b, and further disposed between the two discontinuous portions 540 a,540 b of electrically conductive barrier material.

While FIG. 3 illustrates two electrode portions 330 a, 330 b and asingle portion of electrically conductive barrier material 340, and FIG.4 illustrates two electrode portions 430 a, 430 b and two portions ofelectrically conductive barrier material 340 a, 340 b, and FIG. 5illustrates three electrode portions 530 a, 530 b, 530 c and twoportions of electrically conductive barrier material 540 a, 540 b, itwill be understood that any number of electrodes (or portions ofelectrodes) may be used together with any number of portions ofelectrically conductive barrier material in order to obtain a desiredoperation for any given memory cell.

FIG. 6 illustrates a method 600 of manufacturing one or more phasechange memory cells according to an embodiment of the invention. Themethod 600 may be used to manufacture the memory cells 220, 320, 420,520 illustrated herein, or other similar memory cells.

In operation 602, a first access line (e.g., a word line) may be formed,and in operation 604, a first access line electrode may be formed overthe first access line. In operation 606, a switch (e.g., a firstchalcogenide structure) may be formed over the first access lineelectrode, and in operation 608 a first electrode portion may be formedover the switch. In operation 610 an electrically conductive barriermaterial may be formed over the first electrode portion. In operation612 a second electrode portion may be formed over the electricallyconductive barrier material, and in operation 614 a phase change device(e.g., a second chalcogenide structure) may be formed over the secondelectrode portion. In operation 616, a second access line electrode maybe formed over the phase change device, and in operation 618, the memorycells may be dielectrically sealed and filled. In operation 620, asecond access line may be formed over the second access line electrode.

Referring to the operations 602-620 of the method 600, any suitablemanufacturing method may be used to form the various components. Forexample, the electrodes or electrode portions may be formed bydeposition of materials, including physical vapor deposition (PVD),atomic layer depositions (ALD), chemical vapor deposition (CVD),sputtering, and so forth. Similarly, the electrically conductive barriermaterial may be formed in any relevant manner, including PVD, ALD, CVD,sputtering, and so forth. As mentioned above, in some examples, one ormore of the operations 602-620 may done in situ with one another. Forexample, if the electrically conductive barrier material is Si, it maybe formed in situ with the phase change device so as to prevent the Sifrom oxidizing during, for example, an air break. Alternatively, a shortair break may be taken during which little or no oxide forms, and anyoxide formed may be removed by a subsequent process in some examples. Inother examples, such as where two discontinuous portions of electricallyconductive TiN are used, there may be an air break in between theforming by deposition or other means of the two TiN portions so as tofurther impede the formation of columnar structures. In someembodiments, one or more of the operations 602-620 may be performedusing, for example, photolithographic patterning of components ofindividual memory cells.

FIG. 7 illustrates a portion of a memory 700 according to an embodimentof the present invention. The memory 700 includes an array 702 having aplurality of cells 720 (e.g., PCM cells). Each of the cells 720 includesa phase change device 722 and a switch 724: a phase change storageelement 722 configured to store one or more bits of data, and a switch724 configured to allow data to be selectively read from or programmedin the storage element 722. Each cell 720 is electrically coupled to arespective bit line 750 and a respective word line 770, and is locatedat the crossing of the respective bit line 750 and word line 770 for thecell 720. Each cell 720 may be addressable by selection of theassociated bit line 750 and word line 770. The switch 724 may be aselectable diode or an ovonic threshold switch, as described above withreference to FIGS. 2 through 6 in some embodiments. As illustrated inFIG. 7, the cells 720 are grouped in subsets of four cells in thedirection of the word lines 770. In other embodiments, other subsetsizes may be used, such as subsets having 8, 16, or 32 cells. Ingeneral, the memory cells 720 may be any of the memory cells 220, 320,420, 520 described above, or similar memory cells, and may in someembodiments be manufactured using the method 600 illustrated in FIG. 6(or other, similar method) in some embodiments. While the memory cells720 are typically uniform across the array 702, in some embodiments,different types and structures of memory cells 720 may be used within asingle array 702.

The array 702 may be a 3D array, with cross-point decks, such as thoseshown in FIG. 1 through 5, super positioned over one another in a 3Dcross point memory. Alternatively, the array 702 may be a vertical stackof 2D arrays in order to obtain a 3D array.

To program a cell 720, a programming voltage, e.g., a voltage greaterthan a threshold voltage of switch 724, is provided to the switch 724via the respective word line 770. An inhibition voltage, e.g., a bitline programming voltage, may be provided to the other, unaddressed wordlines 770, thereby preventing a phase state change in the other storageelements 722. In other examples, the cells may be programmed by biasingthe respective bit lines 750 with a programming voltage and providing aninhibition voltage (e.g., a word line programming voltage) to the otherunaddressed bit lines 750. In this manner, any number of cells on arespective word line 770 may be simultaneously addressed in someembodiments.

When a cell 720 is programmed, an electrical current flows through theaddressed cell, thereby heating local chalcogenic material at or above amelting temperature of the material. The chalcogenic material is thenallowed to cool under controlled conditions such that the desired stateof the cell is achieved. More precisely, rapid cooling may place thematerial in the amorphous state that may, for instance, correspond to abinary 0. Conversely, slower cooling may place the material in thecrystalline state that may, for instance, correspond to a binary 1.Intermediate states may be achieved by cooling the material at ratesinterpolated between the rates for cooling used for placing the materialin the amorphous and crystalline states. In some embodiments, heatingthe chalcogenic material at a temperature lower than the meltingtemperature for a particular period of time may place the material inthe crystalline state. Thus, in some instances, a cell 720 may beprogrammed by setting the amplitude and pulse width of the current orvoltage provided to the cell 720 through the word line 770 and bit line750.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited to the specific embodiments of the invention described herein.For example, FIGS. 2, 3, 4, and 5 illustrate various embodiments ofmemory cells 220, 320, 420, 520. However, other embodiments of memorycells may be used, which are not limited to having the same design, andmay be of different designs and include different structure andoperation from the structure and operation of the embodimentsillustrated in and described with reference to these figures. Forexample, as mentioned above, the overall thickness of the electrodeportions and electrically conductive barrier material(s) disposedbetween the phase change device and the switch may vary according to theparticular implementation of a memory cell.

For example, in some embodiments, and with reference back to FIG. 2, ifthe resistance per unit thickness of the electrically conductive barriermaterial 240 is approximately the same as the resistance per unitthickness of the first and second electrode portions 230 a, 230 b, theoverall thickness of the first and second electrode portions 230 a, 230b together with the electrically conductive barrier material 240 in FIG.2 may be approximately the same thickness as the single electrodeillustrated in FIG. 1. In other embodiments, if for example theresistance per unit thickness of the electrically conductive barriermaterial 240 is less than the resistance per unit thickness of the firstand second electrode portions 230 a, 230 b, the overall thickness of thefirst and second electrode portions 230 a, 230 b together with theelectrically conductive barrier material 240 in FIG. 2 may be greaterthan the thickness as the single electrode illustrated in FIG. 1 becausethe first and second electrode portions 230 a, 230 b may be thicker inorder to maintain an overall resistance comparable to the electrode 130illustrated in FIG. 1. In still other embodiments, if the resistance perunit thickness of the electrically conductive barrier material 240 isgreater than the resistance per unit thickness of the first and secondelectrode portions 230 a, 230 b, the overall thickness of the first andsecond electrode portions 230 a, 230 b together with the electricallyconductive barrier material 240 in FIG. 2 may be less than the thicknessas the single electrode illustrated in FIG. 1 because the first andsecond electrode portions 230 a, 230 b may be thinner in order tomaintain an overall resistance comparable to the electrode 130illustrated in FIG. 1. In general, the number and thickness of theelectrode portions and portions of electrically conductive barriermaterial disposed between the phase change device and the switch maygreatly vary from one embodiment to the next.

What is claimed is:
 1. A method of manufacturing a memory cell,comprising: forming a first chalcogenide structure; forming a firstelectrode portion over the first chalcogenide structure; forming anelectrically conductive barrier material over the first electrodeportion; forming a second electrode portion over the electricallyconductive barrier material; and forming a second chalcogenide structureover the second electrode portion, wherein the second electrode portionis disposed between the second chalcogenide structure and theelectrically conductive barrier material.
 2. The method of claim 1,wherein the first chalcogenide structure, the first electrode portion,the barrier material, the second electrode portion, and the secondchalcogenide structure together define a stack with a substantiallyuniform cross section.
 3. The method of claim 1, wherein theelectrically conductive barrier material has a larger cross section thanat least one of the first and second electrode portions.
 4. The methodof claim 1, wherein the first chalcogenide structure is formed over afirst access line and a first access line electrode is disposed betweenthe first access line and the first chalcogenide structure.
 5. Themethod of claim 4, further comprising forming a second access lineelectrode over the second chalcogenide structure and a second accessline over the second access line electrode.
 6. The method of claim 1,wherein the barrier material comprises silicon, and the barrier materialis formed in situ with the second electrode portion.
 7. The method ofclaim 6, wherein the first electrode portion is formed in situ with thebarrier material and the second electrode portion.
 8. The method ofclaim 1, wherein the barrier material is formed by one of physical vapordeposition, chemical vapor deposition, or atomic layer deposition.
 9. Amethod of preventing diffusion between a switch and a phase changememory storage element in a stacked memory cell, comprising:partitioning an electrode disposed between the switch and the phasechange memory storage element into first and second portions; andforming an electrically conductive barrier material between the firstand second portions of the electrode, wherein the electricallyconductive barrier material does react with either the first or secondportions of the electrode.
 10. The method of claim 9, wherein theelectrically conductive barrier material has a substantially differentcrystalline structure than the first and second portions of theelectrode.
 11. The method of claim 9, wherein the first and secondportions of the electrode are at least partially columnar and theelectrically conductive barrier material is amorphous.
 12. A method ofpreventing diffusion between a switch and a phase change memory storageelement in a stacked memory cell, comprising: partitioning an electrodedisposed between the switch and the phase change memory storage elementinto first and second portions; and forming an electrically conductivebarrier material between the first and second portions of the electrode,wherein the electrically conductive barrier material is a first portionof electrically conductive barrier material, the electrode ispartitioned into first, second, and third portions, and a second portionof electrically conductive barrier material is disposed between thesecond and third portions of the electrode.
 13. The method of claim 9,wherein the electrically conductive harrier material is one of titaniumnitride, tungsten silicide, silicon, or combinations thereof.
 14. Amethod, comprising: forming a switch wherein forming the switchcomprises: forming a first chalcogenide structure; forming a phasechange material storage element, wherein forming the phase changematerial storage element comprises: forming a second chalcogenidestructure: and forming a second electrode, wherein the second electrodeis disposed between the second chalcogenide structure and theelectrically conductive barrier material; and forming an electricallyconductive barrier material between the switch and the phase changematerial storage element.
 15. The method of claim 14, wherein formingthe switch further comprises: forming a first electrode over at least aportion of the first chalcogenide structure, wherein the first electrodeis disposed between the first chalcogenide structure and theelectrically conductive barrier material.
 16. The method of claim 14,wherein the electrically conductive barrier material is one of titaniumnitride, tungsten silicide, silicon, or combinations thereof.
 17. Themethod of claim 14, wherein forming an electrically conductive barriermaterial between the switch and phase change material comprises: formingin situ the electrically conductive barrier material, a first electrode,and a second electrode, wherein the first electrode is disposed betweenat least a portion of the switch and the electrically conductive harriermaterial, and wherein the second electrode is disposed between at leasta portion of the phase change material storage element and theelectrically conductive barrier material.
 18. The method of claim 14,further comprising: forming first and second access lines, wherein theswitch, electrically conductive barrier material, and the phase changematerial storage element are disposed between the first and secondaccess lines.